1. Field of the Invention
This invention relates to diagnosing internal combustion engines electronically.
2. Description of the Prior Art
The diagnosis or analysis of conditions and parameters in internal combustion engines has received a great deal of attention in the art over a long period of time. Recent advances in engine diagnostics have tended toward utilization of electronic processing equipment and improved techniques for sensing parameters and conditions on the engine. There are a variety of techniques which may be applicable to engine diagnostics for analyzing particular conditions in the engine, provided measurements can be made of speed profiles of the engine, across an engine cycle, including minute variations in speed which occur within the individual cylinder sub-cycles.
As an example, consider diagnostics which indicate the actual performance of individual cylinders. One measure of engine condition which is known in the art is commonly referred to as relative power contribution; this provides, in a variety of ways, an indication bearing some sort of relationship to the manner in which each cylinder of the engine contributes more or less to the overall power generated by the engine. A most common method or technique used to determine relative power contribution of a spark-ignition engine is selectively defeating the ignition of one cylinder at a time while measuring the decrease in average speed of the engine while each cylinder is defeated, and then comparing, typically on a ratio basis, the loss in average speed attributable to the defeat of the ignition of each cylinder. In non-spark engines (such as diesel engines), it is possible to selectively defeat the injection of fuel into cylinders and provide a similar type of relative power contribution measurement. Ostensibly, the cylinder which causes the greatest decrease in speed, when defeated, is the healthiest cylinder, normally providing the greatest contribution. However, in both spark ignition engines and non-spark ignition engines the instantaneous speed of the engine affects the power stroke of other cylinders, so that these measurements are not as accurate as could be desired.
Thus, a realistically appropriate measurement of relative cylinder power contribution for internal combustion engines has not been available heretofore in the art, since it relies on full-cycle average speed. There are other engine diagnostic techniques which relate directly to speed of an engine, and more particularly to instantaneous, sub-cyclic speed of the engine which permits gathering data relating to the speed variations in an engine which occur on a cylinder-by-cylinder basis, rather than gross or average speed over a full cycle or several cycles. In many instances, such speed measurements may be required during a snap or burst acceleration of the engine whenever the engine cannot be operated on a vehicle disposed on a dynomometer to control speed regardless of the power output of the engine. In other cases, the measurements to be made, similar to the relative power contribution measurements described hereinbefore, have to be made in a time frame relating to the power strokes of the individual cylinders of the engine, which time is relatively small compared with processing of parameters according to complex algorithms. And, even though speed indications can be derived from an engine, they are useless for dynamic engine diagnostics unless they are processed in a time frame which is relatively small in contrast with cylinder firing time of an engine while operating at its maximum speed.